Add additional string validation keywords to rest_validate_value_from_schema

[TimothyBlynJacobs]

I think it'd be helpful to add the minLength and maxLength JSON Schema validation keywords. ​https://json-schema.org/draft/2019-09/json-schema-validation.html#rfc.section.6.3.1

[sorenbronsted]

I will work on this

Added minLength and maxLength validation on strings

Trac ticket: https://core.trac.wordpress.org/ticket/48820

[TimothyBlynJacobs]

Thanks for working on this @sorenbronsted!

Something we need to be careful about is how we are measuring the length of a string. From the RFC:

The length of a string instance is defined as the number of its characters as defined by RFC 8259.

So we need to make sure that the way string length is measured would follow that RFC.

Additionally, it should probably be consistent with JavaScript based JSON Schema validators. I think checking for parity with ​ajv would be a good idea and maybe others as well.

The strings to pay attention to would be things like emoji. From what I can tell, an emoji should be counted as a single character.

• ​https://github.com/json-schema-org/json-schema-spec/issues/215#issuecomment-318156801
• ​https://github.com/json-schema-org/JSON-Schema-Test-Suite/blob/master/tests/draft7/minLength.json
• ​https://github.com/epoberezkin/ajv/blob/master/KEYWORDS.md#keywords-for-strings

This means we should probably be using mb_strlen.

Let's make sure we have tests that cover the same things in the JSON Schema Test Suite as well.

[sorenbronsted]

@TimothyBlynJacobs Thanks for your excellent feedback. I will fix this.

New patch is coming up.

Added feedback from Timothy
Trac ticket: https://core.trac.wordpress.org/ticket/48820

Props sorenbronsted.
Fixes #48820.

Trac ticket: https://core.trac.wordpress.org/ticket/48820

[TimothyBlynJacobs]

In 47627:

REST API: Support the (min|max)Length JSON Schema keywords.

Props sorenbronsted.
Fixes #48820.

Merged in 86cbde3.

Thanks for the PR @sorenbronsted!

Merged in 86cbde3 with some changes to be consistent with our other validation checks.

[TimothyBlynJacobs]

In 47811:

REST API: Add @since entries for rest_validate_value_from_schema().

See #49572, #48818, #44949, #50053, #48820, #49720, #42961, #44975, #43392, #38583.